Electric bed heater



Jun/e l0, 1958 P. o. G. ARALDsEN 2,838,642

' ELECTRIC BED HEATER Filed NOV. l5, 1956 United States Patent O i ELECTRIC BED HEATER Peder Olaf Gothard Araldsen, Sarpsborg, Norway, as-

signor to Sarpsborg Elektriske Fabrikker, Sefa A/S, Sarpsborg, Norway Application November 13, 1956, Serial No. 621,630 Claims priority, application Norway November 15, 1955 6 Claims. (Cl. 219--19) For the electric heating of beds it is most common to use so-called electric heating pads. Such pads of the types w 'ch are commercially available are mostly equipped with two thermostats for reason of safety, but since the heating wire may break and form spark contact it is difficult to achieve an entirely iireproof construction. There is also the risk that the thermostats may remain uncovered while the rest of the heating pad is covered. Heating pads of the`normal sizes available will only heat :a small part of the bed.

There are also known so-called electric heating blankets. These are designed for supplying additional heat while a person is in the bed, and are therefore particularly adapted for sick and old persons who have difficul-l ties in keeping warm by themselves. For preheating a bed before bedtime, especially in a cold room, they are therefore insufficient and inconvenient.

An object of the present invention is to provide an electric bed heater which is adapted for preheating beds with a View to providing a pleasant temperature before one goes to bed, and which at the same time will be entirely iireproof in all normal conditions of use.

With these objects in view the bed heater has an elongated, preferably cylindrical shape, and according to the invention comprises an outer casing having a relatively large diameter, for instance of the order of 80 mm., of a material of relatively low specific gravity, great strength and good electric insulating characteristics, such as paper glued together with water glass, or suitable plastic, and an inner, preferably metallic tube which has a relatively small diameter `and encloses the heating element and which is centered in the outer casing.

Further features of the invention will appear from the lfollowing specification with reference to the accompanying drawings which illustrate a convenient embodiment of the bed heater according to the invention.

Fig. l shows the bed heater in longitudinal section and on a relatively small scale.

Fig. 2 is a cross-sectional view on a larger scale, along the line ll-II in Fig. l.

Fig. 3 is a fractional view in longitudinal section and on the same scale as Fig. 2 of one end portion of the bed heater and with the heating element partly shown in section.

In the drawings 1 is the outer casing, which may have a relatively large diameter, for instance an interior diameter of about 3" or an exterior diameter of 80 mm., and which may conveniently be of a length approximately corresponding to the usual length of a person in the bed, excluding the pillow, i. e. for instance about l---l/z meter. The tube 1 is made of a light and strong material with good electric insulating properties. For instance it may be made of paper wound to a relatively large diameter and glued together, for example with water glass, to a relatively large wall thickness of for example 3-4 mm. The tube is closed in both ends by end plates 2 and 3, which may consist of metal and have Patented June 10, 1958 ICC anges 4 and 5 respectively which engage the outer face of the tube 1.

In the center line of the tube 1 there is mounted a tube 6 which has a considerably smaller diameter, only a fraction of that of the tube 1, and may consist of metal and forms a mechanically strong protecting casing for a heating element 7. The tube 6 is kept centered in the axis of the tube 1 by means of suitable spacing members 8 which may for example be welded thereto. The tube 6 which like the heating element 7 is somewhat shorter than the tube 1 is also retained against axial displacement by means of a bracket 9 welded thereto, which with a bifurcated end portion 10 engages an insulating piece 11 attached to the inside of the plate 2, whereby the tube 6 and heating element are retained in a position in which both ends of the heating element are spaced from the adjacent end plates 2 and 3 respectively,

The heating element 7 is conveniently of the type in which the heating filament is passed back and forth in straight lengths in longitudinal holes 12 in a steatite cylinder 14. By means of terminals 15, 16 on an insulating base 17, attached to the bracket 9 the heating filament 13 is connected to a two-wire installation cable, for instance a P. V. ilat cable 18 which is passed out through the bottom 2 and provided with a plug 19. For mechanical protection the cable 18 may be surrounded by a rubber hose 20 at the point where it passes through the bottom 2 and further inside the same where it is attached to the bracket 9 by means of a tension releasing clamp 21.

That the terminal conductivity of the tube is relatively low, for example if it is made of paper as aforesaid is of no importance in the present case since the conductivity of a down coverlet or other cover or of a bolstered mattress will be far lower. The main thing is that a very strong and light structure is obtained as compared with a casing of metal, and at the same time an additional electric insulation is achieved. A considerable strength is of importance for safety reasons since a tube with a dent in it would be subject to a local heating which might cause fire. As indicated above the outer tube may also be made of plastic or of other strong and light insulating material.

The bed heater is intended to be placed longitudinally in the middle of the bed under the coverlet in the part extending between the pillow and the foot end, and is designed for such a low power consumption of the heating element that the stationary temperature in a usual bed with down coverlet will be for instance about 45 C. at a room temperature of l0 centigrades, i. e. an over-temperature of about 35 centigrades. No thermostat is used since there would be a risk of the thermostat failing with the current turned on or of the tube being placed in a position in which the thermostat is uncovered. Even if the bed heater is wrapped in a down coverlet or an additional down coverlet is placed on top inadvertently, it will not be capable of attaining a dangerous temperature. The eifect in this respect is similar to the reduced effect of added insulation on a tube.

Out of regard to the conditions which may occur in use, it is important completely to protect the heating element against a sinking together of the heating lament in one end of the tube, which might entail a heating effect tending to cause fire. ln this connection it is necessary to calculate with the possibility that the bed heater is taken out of the bed and placed on one end in a corner with a shock without the current being turned off, especially if the plug box is in an inconvenient place. In the embodiment shown, in which the heating filament is passed in straight lengths back and forth in longitudinal holes in a steatite bar, the requirements in this respect are satisfied to a high degree, and failure of the lilament can only cause interruption of the current.

The bed heater is conveniently used in that manner that it is placed in the bed under the cover, preferably several hours, for example at least 2 to 3 hours, before bedtime, or at once when the bed is done in the morning. A suitable power consumption for a satisfactory heating of the bed with dry heat and pleasant temperature may then be about 15 watts, i. e., the consumption of energy during 10 hours will only be about 0.15 kwh. The stationary temperature is attained in the course of some hours and if one should forget having placed the bed heater in position with the current turned on, it may remain there `for an unlimited time without risk.

An important feature of the construction is that the bed heater has a relatively great diameter so that a good heating of the whole bed is obtained without the surface temperature of the outer tube being too high, and it is ensured that small dents or a possible bending of the tube cannot cause undesired local heating.

I claim:

1. An electric bed heater comprising a substantially cylindrical casing of relatively large diameter and of a length corresponding to the length of the major part of a human body and adapted 'for longitudinal placement in a bed between the foot and the head thereof, said casing being formed of a rigid material of low specific gravity and good insulating properties, and end closures for said casing, said casing and said end closures confining an elongated space, an elongated tubular enclosure positioned in said space, said tubular enclosure having relatively small constructional dimensions and extending substantially the whole length of said casing, a heating element y '4 v confined within said tubular enclosure, said heating element being adapted for heating said casing to nondangerous substantially constant temperatures under the heat insulating conditions prevailing in a bed, and spacing means supporting said enclosure and element substantially coaxially Within said casing.

2. Bed heater according to claim 1, characterized in that the heating element comprises an insulating rod having a plurality of longitudinal holes through which the heating filament is passed in straight lengths.

3. Bed heater according to claim l, characterized in that the inner metallic tube is provided with a bracket attached thereto and being in electrically insulating mechanical connection with a metallic end plate for the outer casing.

4. Bed heater according to claim 3, characterized in that the bracket carries an insulating base with terminals for connecting the heating element to a cable.

5. The bed heater of claim 1, wherein the casing is .formed of paper wound to a relatively large diameter and glued together with water glass.

6. The bed heater of claim 1, wherein the casing is formed of paper wound to a relatively large diameter and glued together with a suitable plastic.

References Cited in the iile of this patent UNITED STATES VPariarvrs 567,248 Meek Sept. 8, 1896 1,886,880 Hare Nov. 8, 1932 2,434,188 Winn Jan. 6, 1948 2,565,390 Mitnowsky Aug. 21, 1951 2,712,592 Goldstein et al luly 5. 1955 

